Ferro-ferric oxide-alkali metal ferrate catalyst and its method of preparation



Patented May 24, 1949 OFFICE FERRO-FERRIC OXIDE-ALKALI METAL FER- RATECATALYST AND ITS METHOD OF PREPARATION Max A. Mosesman, Baytown, Tex.,assignor, by

mesne assignments, to Standard Oil Development Company, Elizabeth, N.J., a corporation of Delaware No Drawing; Original application December20, 1946, Serial No. 717,582, now Patent No. 2,455,696. Divided and thisapplication July 29, 1948, Serial No. 41,413

10 Claims. (Cl. 252-474) This invention is directed to a method forpreparing a composition adapted to be used as a catalyst. Moreparticularly, this invention relates to a method for preparing apromoted catalyst for utilization in the hydrogenation of carbon oxides.

This application is a division of U. S. Serial No. 717,582, filedDecember 20, 1946 (now Patent It is well known to the art to synthesizehydrocarbons and oxygenated derivatives of hydrocarbons by passing amixture of carbon monoxide and hydrogen over a suitable catalyst atelevated temperatures and pressures. This reaction is commonlydesignated as the Fischer-Tropsch synthesis and is usually carried outat temperatures lnthe range of about 450 to 675 F. and pressures in therange of 100 120500 pounds per square inch. Such reactions havecustomarily been carried out in the presence of catalysts comprising theoxides of metals in group VIII of the periodic table such as the oxidesof iron, cobalt, and nickel. It is also known to use such oxides ascatalysts either alone or supported on an inert material such asalumina, -kieselguhr, and other such supporting agents. It has also beenknown to add to the active catalytic material in the catalystcomposition a substance ,usually designated as a promoter which exerts aspecific effect on the catalyst activity, selectivity of the reactantsto useful products, and on the active life of the catalyst. Catalystscontaining promoters in substantially small quantities often permitconsistently high conversion of the reactants to desired products overmuch longer periods of operation than is possible when using anunpromoted catalyst.

It is the object of the invention to provide a method for'preparing animproved catalyst. Another object of the present invention is to devisea method for preparing a catalyst particua mixture of Fe(I-I)a and analkali metal hydroxide an oxidizing agent such as bromine, adding thethus formed alkali metal ferrate to the iron or iron oxide catalyst,intimately mixing the two, drying and pilling the mixture, and heatingthe mixture at an elevated temperature of about 1000 F. in the presenceof air to obtainv the finished catalyst. Following the heat treatment inthe presence of air, the'catalyst is then reduced at a temperature inthe range between 700 and 1600 F.

The alkali metal'ferrate promoter, for example, potassium ferrate to beadded to the catalyst may be prepared in a number of ways. In thepreferred procedure, Fe(NOc)3.9H2O is reacted with ammonium hydroxide tocause the precipitation of Ii'e(0H) sand the ferric hydroxide larlyadapted for use in the Fischer-Tropsch syn- .as involving thepreparation of a catalyst com-.

prising a major portion of iron or an iron oxide as the active catalyticmaterial and a minor portion of an alkali metal ferrate such aspotassium (KzFeOO as the promoting material. The method of preparationcomprises the steps of forming an alkali metal ferrate by adding to thusformed is filtered and then slurried with water. The water slurry isadmixed with solid KOH and'to the mixture is added slowly liquid bromineand solid KOH until the mixture is saturated with respect to the latter.The reaction mixture should be kept at a temperature. below about F. Themixture may then be heated carefully with stirring for about one-halfhour at. about 140 F., allowed to cool, and the top layer removed fromthe reaction mixture. The top layer is dried in a vacuum and then washedwith alcohol until substantially free of alkali. The alcohol-washedmaterial is also dried in a vacuum to produce a potassium ferratesubstanv potassium ferrate be added to the active catalytic materialsuch that the finished catalyst will comprise about 0.2'to 20 weight percent potassium ferrate based on the iron or iron oxide employed. Themixture of potassium ferrate and iron or iron oxide is milled,preferably in the presence of a small amount of alcohol, dried at'atemperature of about 230 F. and\pilled. The pilled material is thenheated at superatmospheric temperatures in the presence of air to obtainan active catalyst containing promoting quantities of potassium ferrate.i

The presence of both potassium bromide and potassium bromate in smallamounts in the finished catalyst is not objectionable since both ofthese substances may have a. tendency to promote the activity of theiron oxide. catalyst in the hydrocarbon synthesis reaction.

by weight of Fe(NO3)3.9H2O is added 90 parts by weight of NH4OH. Theprecipitated Fe(OH)3 is filtered dry and then slurried with about 100parts by weight of distilled water. To the slurry is added 50 parts byweight of solid KOH and while the suspension is maintained at atemperature below 140 F., 50 parts by weight of liquid bromine and solidKOH are added. During this addition, the materials are added graduallywith continual stirring. Suflicient solid KOH is added to the reactionmixture so that the latter is completely saturated with respect to thealkali. At this point, it is preferable to add an excess of solid KOH tothe mixture, for example, parts by weight of excess alkali, beforeheatingthe mixture with stirring at a temperature of 140 F- forapproximately one-half hour.

The heated mixture'is allowed to cool and the top layer comprisingpotassium ferrate is decanted from the total mixture and dried underpartial vacuum. Alkaline material remaining in the dried potassiumferrate may be removed by successive washings and decantations withalcohol. The potassium ferrate is then redried under vacuum and, asproduced in this manner, is substantially free from alkalinecontaminants and contains minor portions of potassium bromide orpotassium bromate as illustrated by the following analysis:

Percent K2FeO4 75.0 KBr 20.0 KBrOa 5.0

milling, dried at about 230 F. and pilled to a size desired forsubsequent use in the synthesis process. The pilled material is thenheated in free excess air at about 1000 F. for about 4 hours and allowedto cool.

The beneficial results to be obtained by using the above-preparedcatalyst, containing 5 parts by weight of potassium ferrate per 100parts by weight of ferro-ferric oxide in the hydrogenation of carbonmonoxide is exemplified by th following data:

The catalyst prepared in accordance with the above procedure is placedin a reaction chamber and reduced in the presence of hydrogen for 24hours at a temperature of 700 F. and atmospheric pressure. The hydrogenis passed over the catalyst at a rate of 1000 volumes of hydrogen pervolume oLcatalyst per hour. A synthesis gas mixture comprising one partof hydrogen per part of carbon monoxide is then passed over the catalystat a pressure of 150 pounds per square inch gauge, a temperature of 575F., and a rate of 200 volumes per volume of catalyst per hour.

This catalyst was employed in the synthesis of hydrocarbons from carbonmonoxide and hydrogen for 1736 hours. Samples of the products wereexamined during each 24 hour period. During the first 508 hours the COconversion in mole per cent declined from an initial figure of 97.9 to91% while the selectivity ratio of C4 and heavier hydrocarbons producedto total product in mole per cent increased from 'an initial figure of64% to as much 78% and after 508 hours operation was 73.1%. During thisperiod of time, the yield of 04+ bycarbon monoxide consumed variedwithin a wide range from at the outset to as high as 250 after 220hours, 257 after 244 hours, and had only declined to in the interimbetween 484 and 508.

hours.

The amount of water produced during this period in cc. per cubic meterof hydrogen and carbon monoxide consumed also varied widely ranging fromabout 12 to about 60 and averaging between 36 and 48. During all thistime of operation, the test data on the hydrocarbons produced in theprocess showed the presence of a considerable amount of alpha olefins.alpha olefins is considered to be very beneficial in that the alphaolefins are valuable feed stocks for polymerization to high molecularweight polymers useful as lubricating oils. The ratio of alpha to betaolefins produced during the first 508 hours of operation ranged fromabout 4.6 to as high as 4.7 and the sample obtained just previous to theend of the first 508 hour period showed an alpha olefin to beta olefinratio of 4.3.

Up to 998 hours operation the carbon monoxide conversion in mole percent slowly declined from 91 to 82.5 while the selectivity ratio of C4+hydrocarbons to total product in mole per cent remained fairly constant,the data showing a 74.6% selectivity after 998 hours operation with theimproved catalyst of the present invention. The yield of 04+hydrocarbons in cc. per cubic meter of hydrogen and carbon monoxideconsumed after 508 hours was 185 and after 998 hours was still 185; somefluctuation of yields during this period was observed with as much as228 cc. of Cu hydrocarbons being produced per cubic meter of hydro- Igen and carbon monoxide consumed with the greater amount of the datashowing the produc-' tion to vary between 170 and cc. The amount ofwater produced during this period of time was in the range from about 24to 42 cc. per cubic meter consumption of hydrogen and carbon monoxide.

The ratio of alpha to beta olefins declined slightly during the periodto below 3.3.

The improved catalyst of the present invention was continued in use witha slight decline in activity and selectivity until after 1088 hours thecatalyst was reduced with hydrogen at 700 F. for 24 hours at 1000v./v./hr. and at atmospheric pressure. After this treatment, thecatalyst was again used in the synthesis of hydrocarbons from hydrogenand carbon monoxide for a total of 1736 hours.

After the treatment subsequent to 1088 hours employment as catalyst themole per cent carbon monoxide conversion was raised to 99.4 while theselectivity ratio of Cd" hydrocarbons to total product was 70.7%. Theyield of 84+ hydrocarbons after the foregoing treatment showed only 149cc. per cubic meter of hydrogen and carbon monoxide but increased withinthe next 24 hour period to 203 then in a second 24 hour period to 262and remained in the neighborhood of 200 and higher until 1256 hourstotal operation had ensued. The carbon monoxide conversion declined from94 mole per cent after 1256 hours to 90.1 after 1424 hours and to 89.8after 1472 hours. After the catalyst had been used for a total of 1520hours, it was then given a similar reduction The presence of w i e 1 I nwas raised after 628 hours of operation to 585' I".

and in the'periodbetween 700 hours until the end of the run wasmaintained at 600 F.

While the foregoing run was terminated after 1736 hours! it is believedthat the improved catalyst could have been used for even longer periodssince, subsequent to the run termination, the synthesis. gas feed to thereactor was found to 'contain '17 P. ,P. M. of sulfur as H25. More than5 P. P. 'M. of sulfur has been found to poison the anda feed rate of200'v./v./hr. This temperature j:

an -no- A weighed amount of material having the above composition wasthen suspended in 95% ethyl al- I 'cohol to which was added a weighedamount of ferro-ferric oxide which was thoroughly mixed by-stirring .toform a smooth slurry. The. slurry was dried in an oven at 95 C. with air'circulating freely for a period of 48 hours. The temperature was thenraised to about 110 C. and-maintained, with the exception of a 12 hourperiod activity of the catalyst in synthesizing hydrocarbons.

It will be apparent from the foregoing data that the improved catalystof the present invention may be used for periods up to 1000 hours andhigher while yet obtaining substantial conversion, selectivity, andyield of C4 and higher hydrocarbons. While not mentioned in theforegoing de-' scriptionof the run, the amount of oxygenated material inthe hydrocarbons produced was maintained at a low figure throughout therun.

In contrast to the above run, an unpromoted ferro-ferric oxide catalystoxidized in the presence of air and subsequently reduced underatmospheric conditions described above was employed under similar runconditions. The selectivities and yields of useful products wereconsiderably lower for the unpromoted catalyst than were obtained in thecase of the promoted catalyst. For example, the unpromotedcatalyst per-I In another example, 340 parts of Fe(NOs)3.9H2O was dissolved indistilled H2O. A dilute solution of NH4OH was added to the solution toprecipitatev temperature. To the cooled material 50 parts of bromine wasadded below the surface of the solution whil stirring vigorously. SolidKOH was then added in small quantities until saturation During theaddition of the KOH the'temperature was maintained no higher than 41 C.and at approximately C. The solution was then carefully heated to 60 C.for one-half hour, heat. removed and the solution cooled. Afterapproximately 24 hours, the upper half of the material, hereafterreferred to as the upper layer, was removed. The upper layer and thebottom half, referred to as the lower layer, was then evaporated undervacuum at a temperature of 47 C. for two weeks. After this period boththe upper layer and the lower layer were removed from the heat treatingoperation and washed free of KOH by repeated separate washings with 95%ethyl alcohol. The washed samples were filtered and dried under avacuum. The upper layer was analyzed as follows:

. Per cent FezOa 62.5 KsFeO4 37.5

' feed stock, the conditions of operation being Q was obtained with theKOH being added to excess.

when the temperature rose to about 160 Ci, for three weeks. The driedmaterial was pilled into /a inch pills which were heated for 4 /2 hoursin the presence of an oxygen-containing atmosphere at 1000' F. followingwhich the material was allowed to cool in air to atmospherictemperature.--

The catalyst prepared in the foregoing manner comprises 2% by weightKaFEOA and 98% iron oxide and was then employed for the synthesis ofhydrocarbons from carbon monoxide and hydiiogen :after being reduced inthe presence of hydrogen for 24 hours at a temperature of 700 F. and atatmospheric pressure. During the reduction treatment the hydrogen waspassed over the catalyst at the rate of 1000 volumes of hydrogen pervolume of catalyst per hour. -A synthesis gas mixture comprising onepart of hydrogen per part of carbon monoxide was employed as the 150,.pounds pressure, a temperature of 575 F and a feed rate of 200 volumesof feed per volume of catalyst'per hour.

tive yie ds of C4 and heavier hydrocarbons could be obtained, with theimproved method of obtaining the catalyst, for over 600 hours. Duringcertain periods of the operation as .much as 307 cc. of

C4 and heavier hydrocarbons per cubic meter of feed consumed wereobtained. During longer.

periods, 04 and heavier hydrocarbon yields ranging from approximatelycc. to 237 cc. per cubic meter of feed stock consumed were obtained.

It is seen,.therefore, that the catalyst composition produced inaccordance with my process isgreatly superior to a catalyst which hasnot been promoted with potassium ferrate. v

While examples of temperature and pressure conditions suitable for usein the practice of the present invention have-been given to illustrateits advantages, it will be obvious to workers skilled in the art thattemperatures and pressures over a substantial range may be employed andgoodresults obtained. It will also be obvious that the promotingmaterial admixed with the iron or iron oxide catalyst may be. presentover asubstantial range and satisfactory results obtained. It is notintended that the above-cited examples limit the scope of my invention.

The practice of the invention has been illustrated by the employment ofpotassium ferrate as the alkali metal ferrate in preparing the catalyst.It is within the scope of the invention to use other alkali metals thanpotassium in preparing the catalyst adapted for use in the Fischer-Tropsch synthesis. For example, sodium and lithium ferrate may be usedin lieu of the potassium ferrate. Potassium ferrate, sodium ferrate, andlithium ferrate may be used, preferably in they order given, inpreparing the catalyst. The

.lithium ferrate will be less desirable to employ cc of the presentinvention, what I wish to 7 claim as new and useful and to secure byLetters Patent is:

1. A method for preparing a catalyst adapted for use in aFischer-Tropsch synthesis which consists of the steps of preparing anadmixtur of term-ferric oxide and alkali metal ierrate in an amount inthe range between 0.2 and 20% by weight of said ferro-fer-ric. oxide.heating said admixture at a-superatmospheric temperature of about 1000F. for about 4 hours in the presence oi an oxidizing atmosphere, andsubsequently contacting the admixture with a reducing atmosphere at asuperatmospheric temperature in the range between 700 and 1600 F. forabout 24 hours.

2. A method of producing a catalyst suitable for use in theFischer-Tropsch synthesis which consists of the steps of forming analkali metal ferrate substantially free from contaminating materials,admixing the alkali metal ferrate with ierro-ferric oxide in an amountsufllcient to form an admixture containing between 0.2 and 20% by weightof alkali metal ferrate based on the ferroferric oxide, heating theadmixture in the presence of an oxidizing atmosphere at asuperatmospheric temperature of about 1000 F. for about 4 hours andsubsequently reducing the heated mass in a reducing atmosphere at asuperatmospheric temperature of about 700 F. for about 24 hours.

.3. A method in accordance with claim 2 in which the alkali metalferrate is potassium terrate.

4. A method in accordance with claim 2 in which the alkali metal ferrateis sodium ferrate.

5. A method in accordance with claim 2 in 'which the alkali metalferrate is lithium terrate.

6. A composition adapted for use as a catalyst in the production ofhydrocarbons and oxygenated hydrocarbons which consists of a mixture offerro-ferric oxide in an amount in the range between 80% and 99.8% byweight and an alkali metal ferrate in an amount in the range between 0.2and by weight whichmixture has been contacted with an oxidizingatmosphere at a temperature of about 1000? F. for about 4 hours and thenwith areducing atmosphere at a temperature in the range between 700 and1600 F. for about 24 hours.

'7. A composition in accordance with claim 6 in which 'the alkali metalferrate is potassium Ierrate.

8. A composition in accordance 'with claim 6 in which the alkali metalferrate is lithium fermixture of approximately by weight of ferro-ierricoxide and approximately 5% by weight of potassium ferrate which mixturehas been heated in the presence of air at a temperature of the order of1000 F. for about 4 hours and then heated in the presence of hydrogen ata temperature of about 700 F. for about 24 hours.

MAX A. MOSESMAN.

No references cited.

